The present invention relates to a process for synthesis of high quality superconducting magnesium diboride (MgB2) powders.
Recently, magnesium diboride (MgB2) was found to exhibit superconducting properties. It is thought that MgB2 may be an alternate to conventional superconductors such as NbTi or BSCCO in the 20-30K and 0-1T range for the fabrication of conductor tapes or wires. That has naturally lead to investigation into optimal processes for preparing this material. Prior processes for producing MgB2 powders generally have described the use of stoichiometric amounts of magnesium and boron, i.e., Mg:B of 1:2 (e.g., Cunningham et al., Physica C, v. 353, pp. 5-10 (2001)), have heated such mixtures under vacuum or under a hydrogen/argon mix, have used quartz tubes, or have required high pressure techniques to obtain the desired MgB2.
Other prior processes have included a process wherein boron filaments are exposed to magnesium vapor and processes involving deposition of magnesium diboride via magnetron sputtering, pulsed laser deposition and the like. Just recently, Aswal et al. (Physica C, v. 363(#3) pp. 149-154, Nov. 15, 2001) have described a process that involves Mg excess to avoid Mg loss during the synthesis. However, they mixed boron and magnesium powders and pressed the mixture into pellets and did not produce MgB2 powder with good superconductive properties.
Despite these prior processes, an improved process for preparing magnesium diboride powder has been desired. After extensive and careful investigation, a process has now been found in the preparation of magnesium diboride powder. In particular, the present process involves heating amorphous boron powder pressed in pellets and solid magnesium under an inert atmosphere in a Mg:B ratio larger than about 0.6:1 at temperatures and for a time sufficient to form superconducting magnesium diboride. Note that the solid magnesium pieces (e.g. turnings or shavings) were not mixed with the boron powder in this invention. This leads to high quality MgB2 superconducting powders since the impurities and MgO in the magnesium metal would not be left inside the MgB2 powder after its synthesis.
It is an object of the present invention to provide a process of preparing high quality superconducting magnesium diboride.
It is another object of the present invention to provide stable superconducting magnesium diboride compositions.
It is another object of the present invention to provide a process, which allows the formation of Mg(B,O) precipitates inside MgB2 grains that act as flux pinning centers in magnetic field.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a process of preparing superconducting magnesium diboride powder by heating amorphous boron powder and solid magnesium under an inert atmosphere in a Mg:B ratio greater than about 0.6:1 at temperatures and for time sufficient to form said superconducting magnesium diboride.